assume cs:code
code segment
    start:mov ax, 0b800h
          mov es, ax
          mov ah, 'a'

      s: mov es:[160*12 + 40 * 2], ah
         call delay
         inc ah
         cmp ah, 'z'
         jna s

         mov ax, 4c00h
         int 21h
    
delay:  push dx
        push ax
        mov dx, 1000h
        mov ax, 0
    s0: sub ax, 1
        sbb dx, 0
        cmp ax, 0
        jne s0
        cmp dx, 0
        jne s0
        pop ax
        pop dx
        ret

code ends
end start
